This invention relates to a zinc plated steel plate having an improved solderability, and this invention also relates to various cans such as 18 liter-cans, paint cans, oil cans and the like which are produced from said zinc plated steel plate using ordinary soldering techniques. The zinc plated steel plate of this invention having an improved solderability is a zinc electroplated steel plate, zinc vapour deposited steel plate or molten zinc-plated (galvanized) steel plate plated by the use of a molten zinc plating bath containing easily oxidizable elements such as aluminum, the solderability of which is improved by making the surface substantially free from oxides and coating an anti-rust film on the oxide-free surface to keep the surface free from oxides.
Heretofore, a tin-plated steel plate (hereinafter referred to as "tin-plate") has been used as a starting material to produce various cans by the use of solder. However, recently, tin resources have been exhausted worldwide and the price of tin plate has suddenly risen. Accordingly, the development of other starting materials having satisfactory solderability and anti-corrosive properties on the same or a higher level in comparison with tin plate is in high demand. In order to satisfy this demand, a steel plate having a thin metallic chromium layer and chromic acid film, i.e. a tin free steel plate, has been developed and used as a starting material to produce cans.
This tin free steel plate has the same or better anti-corrosive properties and paintability for baking paint and its price is lower in comparison with tin plate.
However, the solderability of this plate is much poorer than that of tin plate. This is a great disadvantage of this plate. Therefore, when manufacturing cans using the tin free steel plate, it is necessary to employ a seam welding technique or other special bonding techniques using a bonding agent such as seam cement on its bonding counter part.
On the other hand, in order to produce cans on a mass production scale, an operating efficiency and production efficiency equivalent to those in the present tin plate can producing process are required, and complete soldering must be carried out by the can producing equipment using the present automatic soldering system. The above mentioned seam welding technique or other special bonding techniques emploued to produce cans from the tin free steel plate is poorer with respect to working efficiency, and production efficiency and cost than the conventional soldering technique, and also creates various problems with respect to production equipment. Under these circumstances, the development of new and cheap can materials is desired, which do not give rise to the above mentioned various problems as in the case of the bonding of tin free steel plate, and which can be substituted for the conventional tin plate.
If the new material as mentioned above can be developed, the material will be widely used not only as a starting material for cans but also for various other uses where appropriate solderability is required, for example chassis of light electrical appliances such as radios, televisions and the like.
For the purpose of research for new material which does not have the above mentioned disadvantages and which can be favourably used as a starting material to produce various cans such as 18 liter cans, we have tested many various surface treated steel plates with respect to properties for can material. As a result of this research, we have found that a zinc electroplated steel plate, zinc vapor deposited steel plate, or galvanized steel plate plated by the use of a molten zinc plating (galvanizing) bath containing easily oxidizable elements such as aluminum, having solderability improved by making the surface substantially free from oxides and coating an anti-rust film on the oxide-free surface, is an excellent can material. The zinc plated steel plate thus treated has solderability equivalent to that of tin plate, and is better in respect of corrosion resistance and price than tin plate.